Two out of three pregnant women in the U.S. take some kind of medicine during pregnancy. Yet very few drugs are tested in pregnant women.

What data now exists comes from two sources:

Pregnancy registries, mostly maintained by drug makers, that collect reports from pregnant women using various medications.

Animal studies. However, drugs may be safer or more dangerous to humans than to the animals used in the studies.

Now comes the Medication Exposure in Pregnancy Risk Evaluation Program (MEPREP). The program is a collaboration between the FDA, Kaiser Permanente, Vanderbilt University (using Tennessee Medicaid data), and a consortium of HMOs called the HMO Research Network Center for Education and Research in Therapeutics (managed by Harvard University).

The study will analyze health care data on about 1 million U.S. births from 2001 to 2007. The idea is to gather information on all medications prescribed for pregnant women and to look for health effects and birth outcomes.

"Results of these studies will provide valuable information for patients and physicians when making decisions about medication during pregnancy," Gerald Dal Pan, MD, director of the Office of Surveillance and Epidemiology at the FDA’s Center for Drug Evaluation and Research, says in the news release.

Until the data become available, women and their doctors will have to make their own decisions on whether a drug provides enough of a benefit to pregnant women to override concerns about possible risk.